Motor vehicles are sometimes subject to very stringent pollutant emission limits. In order to meet current and in particular also future emission or exhaust limits, accurate fuel metering during injection, among other factors, is very important.
However, it must be taken into account that various tolerances are present during the metering. Such metering tolerances generally result from sample-based needle dynamics and the sample-based static flow rate of the fuel injectors. An influence by the needle dynamics may be reduced, for example, by a mechatronic approach such as so-called controlled valve operation. In controlled valve operation, activation times of the fuel injectors are adapted in the sense of a regulation, for example over the service life of a motor vehicle.
Possible errors in the static flow rate result from tolerances in the injection hole geometry and the needle lift. The injection hole geometry is often optimized for good emission values, although this may increase the sensitivity to carbonization. Thus far, it has usually been possible to correct such errors only globally, i.e., with regard to all fuel injectors of the internal combustion engine together, based on lambda control or mixture adaptation, for example. However, it cannot then be recognized whether individual fuel injectors of the internal combustion engine have a deviation with regard to their static flow rate (i.e., the fuel injectors deliver different quantities for the same opening duration), which may be relevant to exhaust emissions or smooth running.
A method is described in, for example, German Patent Application No. DE 10 2015 205 877 for ascertaining a static flow rate of a fuel injector or a value that is representative of same.